Cryptographic technique and apparatus



Nov. W 1964 w. R. HUGHES ETAL 3,156,051

CRYPTOGRAPHIC TECHNIQUE AND APPARATUS Filed June 6, 1961 LENS RANDOM DOT MASK \2 LIGHT SOURCE CARD \5 N M A T R F A H 0 N ewm R um oD m mm A L M @P Mr w m W@ W PHOTO6RAPH\C CODED MESSAGE \5 United Sates Patent 3,156,051 CRYPTGGRAPEHC TECHNIQUE AND AIFPARATUS William R. Hughes, Northridge, and Robert M. Stewart, Err-ciao, Caiifl, assignors to tippers-General Qorporation, Glendale, Caiih, a corporation Fiied dune 6, 1961, fier. No. 115,153 9 Claims. (Cl. 35-2) The present invention relates in general to the cryptographic arts and more particularly relates to coding and decoding apparatus using optical and photographic techniques.

There is an ever-existing need for cryptographic techniques by means of which a message can be enciphered or encoded with the knowledge that the enciphered message is secure. By secure it is meant that in the event the message is intercepted, the interceptor would find it extremely difficult if not impossible to decipher the message and thereby learn its contents. The present invention provides such cryptographic security.

In accordance with the present invention, message data is sampled over small areas thereof, the samples thusly taken being distributed over a large area such that all of the information sampled in the small areas is scrambled in a common large area. More particularly, in accordance with a preferred embodiment of the invention, a code plate is produced that is subdivided into a relatively large but predetermined number of smaller areas, each of the smaller areas containing within its boundaries what appears to be a random arrangement of dots. The dots may be opaque or transparent and are located differently in their respective areas, that is to say, if all the smaller areas were somehow superimposed one upon the other, no two dots of all those employed would be in registration. The code plate is interposed between a lens mosaic and a source of message information which projects the information against the code plate, the lens mosaic respectively including as many lenses as there are small areas on the code plate. The message information is sampled by the small dots in each small area of the code plate, the plurality of samplings thusly taken by each code plate area being projected through the associated lens in the lens mosaic onto a large common area in the form of a photographic plate. In other words, the formal message information has been converted to a large number of dots interlaced with each other in a seemingly random nature. The photographic plate thus contains the enciphered message. To obtain the original formal message once again, it is now necessary to project the random arrangement of dots on the photographic plate back through the lens mosaic and the code plate onto a new photographic plate upon which the dots legibly rearrange themselves into the original message.

It is thus seen from what has been said that all three elements, namely, the code plate, the lens mosaic, and the photographic plate upon which the message is enciphered are needed for deciphering purposes. Consequently, if the photographic plate is somehow intercepted, the message could not be deciphered unless the other two of the mentioned elements are also obtained. Hence, as mentioned previously, the present invention provides a very secure system of message encryption.

It is, therefore, an object of the present invention to provide a very secure cryptographic system.

It is a further object of the present invention to provide a cryptographic system that uses optical, photographic and sampling techniques to insure substantially foolproof encryption.

It is a further object of the present invention to provide a system of message encryption in which several of the system elements, including the element containing the en- 3,156,051 Patented Nov. 10, 1964 "ice ciphered message, are required for deciphering purposes, thereby providing for secure message encryption.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

FIG. 1 is a schematic presentation of the manner in which the code plate is prepared;

FIG. 2 schematically illustrates the manner in which a message is encoded;

FIG. 3 schematically illustrates the manner in which a coded message is decoded; and

FIG. 4 illustrates the technique used to manufacture certain dot cards which, in turn, are used to manufacture the code plate.

Considering now the drawings for greater details of the invention, reference is made first to FIG. 1 wherein is illustrated the preparation of the code plates. As shown, a code plate 10 is prepared utilizing a lens mosaic 11, a mask 12, and a source of random dots 13. A source of light (not specifically shown) is also required, preferably a diffused light source. The lens mosaic consists of a large number of small individual lenses mounted in a plane, such as lens 11a, only a few of the lenses in the mosaic being shown for sake of simplicity. The mask is used to mask off or shield all lenses except one during the code plate preparation and for this purpose the mask basically consists of an opaque plate having an opening 121; therethrough having approximately the same dimensions as an individual lens in the mosaic. As for the source of light, it is used to illuminate the random dot card so that the random dots may be focused onto the code plate through the lens in the lens mosaic that is in registration with opening 12a in the mask. The focusing of the random dots through the lens and onto the code plate is illustrated by means of broken lines 14a and 14b. The code plate itself is photographic film or photographic glass plate so that the random dots are thus photographed on the small area of the code plate that faces the lens through which the random dots are focused. In the instance shown in the figure, the random dots are recorded on the small area facing lens 11a.

Having recorded the random dots of card 13 on an area of code plate it), the random dot card is then replaced by a new card having a new set of random dots and, at the same time, mask 12 is moved to a new position so that its opening exposes another of the lens in lens mosaic 11. At this point, the steps previously delineated are repeated once again, at which time the random dot card is again replaced and mask 12 again moved to a new position. This process is repeated until all the areas of the code plate have been exposed. The random dot cards are always placed in the same position when the exposures are made, with the result that at the end the code plate consists of a large number of photographed dots equal in number to the sum of the dots on all the random dot cards. Hence, if the mask was now removed and light projected through the developed code plate back onto a blank card put in the position of the random dot cards, all the dots that had been previously exposed would be reproduced.

Having described the method by which a code plate is produced, reference is now made to FIG. 2 wherein is shown the manner in which such code plate is used in the system. More specifically, after being photographically developed, code plate 1t? is placed in the same position relative to lens mosaic 11 that it had when exposed. Sensitive photgraphic film 15 is placed in the position previously occupied by each of the random dot cards. Lens mosaic 11 is also once again required and is positioned as it was for the preparation of the code plate. In enciphering a message, the first step is to project the message information against the outside surface of code plate 10. While a number of techniques for doing so are available, the message may be projected against the code plate by preparing the message on translucent paper andthen placing the paper next to the code plate. A source of light is then used to illuminate the message and, in consequence thereof, the message is sampled by the dots on the code plate. It will be obvious that if the original dot on the random dot cards were black, the developed code .piate will appear tobe full of holes, that is, each black dot on the random dot cards will appear as a clear or transparent area on the developed code plate. This is now used to sample the message and the sam pled data is then projected through all the lenses of lens mosaic 11 onto photographic film 15. The data samples projected by each lens are distributed over the complete area of the photographic film as a series of dots so that all of the data is completely scrambled. The scrambling pattern, of course, depends upon the arrangement of the dots on the original random dot cards. The fact that the scrambled data on each small area of code plate It) is projected through its associated lens in lens mosaic 11 onto the entire area of photographic film 15 is clearly illustrated in FIG. 2 by means of the broken lines, such as broken lines ldaand 16b.

It will be recognized that the message, as coded, is completely unintelligible. To decode the message a reverse process must be employed as shown in PEG. 3 to which reference is now made. Specifically, light is used to illuminate photographic film 15 on which the message is recorded in coded form, the messagethereby being projected by lens mosaic 11 onto code plate 10. Stated differently, all of the dots that are in the codedmessage are projected onto the code plate by the lens mosaic. Code plate 10, however, selects out or passes only those dots which correspond to that part of the message that was originally in the area of focus for each individual lense in lens mosaic 11. As a result, all of the data is separated out and by use of a translucent screen 17, the data can now be reader by use of a photographic film the reproduced message can be recorded.

From the above description, it will be obvious that the random dots onthe random dot cards must be carefully placed. The requirements for these dots are that no two dots on the different cards ever appear in the same position on those cards. This requirement is to maintain the codes orthogonal and thus prevent cross-talk from one part of the message to another part. If the dots did overlap the same position on the different cards, the decoded message would appear degraded and noisy so that the above statement of no dots appearing in the same position is a requirement for no message cross-talk or a minimum of it. Furthermore, the number of random dot cards must be equal to the number of lenses in the lens mosaic and the ratio of the area of dots to the surrounding area around the dots must be approximately equal to the reciprocal of the numberof-lenses for efficient data transmission and minimum cross-talk. Since the dots on the dot cards represent the code, this code should be one in which the dots are fairly evenly distributed across the complete area of the card in order to insure a uniform sampling of the message data.

'One method of preparing the dot cards is illustrated in FIG. 4 and involves dividing each card into equal'areas, such as, for example, area 18, the number of equal areas being the same as the number of lenses in lens mosaic 11.

One dot is then placed in each of areas 18 in a random fashion. The position of a dot is selected at random and as each position is used it is never used a second time.

Each area 18 is subdivided into smaller areas, such as, for

example, smaller area Eli, as shown in the figure, the dot being systematically located on each card in a new position in the sub-area. By way of example, the code can be represented as C in which a and [3 represent the position of an area and 'y and 5 represent the position of the dot within one of the areas. The requirement then is that in any one dot card all possible as and Bs be used but that for a given set of as and ,8s the value of 'y and 6 be picked at random. There is the further requirement in going from one dot card to the next that for any given value of a and ,8 that v and 6 never be repeated, thereby assuring that no duplicate dots ever appear. The actual selection can be done by hand, keeping track of all the values of a, ,8, 'y and 6, or-it could be done automatically by programming a digital computer.

As mentioned previously, the principal use of a system such as has been described would be in the coding of message information which is normally in printed form. However, the system could also be used for coding electrical signals since these signals could be projected as input data by means of a cathode ray oscilloscope or television presentation. The photographic film of FIG. 2 could, or" course, be a television pick-up tube for picking up the coded data. In using this system for electrical data decoding, the coded message of FIG. 3 would be replaced with a cathode ray tube display and the translucent screen or film would be replaced with an iconoscope or other type of pick-up tube.

It should also be mentioned that a distinct advantage of this invention is that the coded message can be made extremely complex. The information can be completely intermixed so that unscrambling would be essentially impossible without use'of the original code plate. In this respect, since the dots on the original random dot cards are fairly uniformly distributed on each card, the message information when coded will be uniformly distributed, which means that a coded message will look like a random dot pattern. Moreover, a cryptographic system constructed and used in accordance with the present invention offers the opportunity of quickly and easily changing the code since it is only necessary to remove one code plate and replace it with another to change the code. Thus, a high degree of security can at all times be maintained with any such system.

The system also has the additional advantage that when used in its electrical configuration as described earlier, the message data, when coded, will appear as fairly uniformly distributed data even though the original message was very non-uniform in its distribution. As an example, a message which consists of a single black dot inthe center of a white background will be uniformly distributed to a large number of small black dots on a white background by the coding process. This is equivalent to transforming a single message pulse, which occupies a short time duration, into a large number of randomly distributed pulses which occur over a long period of time. Thus data which occurs in short bursts is almost evenly distributed over a long period of time. The advantage here is that short burst data which would normally occupy a very large bandwidth for its transmissioncould be spread out in time. Those times between message data when no transmission occurs would thus be utilized. This then approaches the ideal coder in which information occurring at a non-uni form rate is coded into information occurring at a uniform rate.

Having thus described the invention, what isclaimed is:

1. Coding apparatus comprising: a photographic plate for recording images projected thereon; a lens mosaic having N lenses, N being an integer greater than 1, said mosaic being positioned in front of said plate whereat said N lenses will respectively project upon N different areas thereof; means for projecting N different; patterns of randomly arranged images of dots on each of the N areas of said plate, the projection by said means being such that the arrangements of dot images in said N areas are different from each other, and means for recording on a medium in superimposed relationship in a single area a data pattern as modified in each discrete N area by the respective arrangement of dots in said N areas.

2. The coding apparatus defined in claim 1 wherein said means includes N flat members on which dots are randomly arran ed in respectively N different patterns; and a mashing element interposed between said members and said mosaic, said masking element having a single opening therethrough for limiting the projection of the dots on a member to a single selected lens.

3. The coding apparatus defined in claim 2 wherein said members are opaque cards and the dots thereon are small holes for permitting light therethrough.

4. The coding apparatus defined in claim 2 wherein said members are photographic film negatives on which the randomly arranged dot patterns are respectively recorded.

5. Coding apparatus comprising: a first photographic piate positioned in a first plane and having N diflerent areas upon which N different patterns of randomly arranged dots are respectively recorded, N being an integer greater than 1; a second photograhpic plate positioned in a second plane for recording patterns of light incident thereon; a lens mosaic positioned in a third plane between said first and second planes and having a plurality of N lenses in registration, respectively, with the N areas of said first plate, said mosaic being further positioned so that said N different patterns of dots are respectively projected by said N lenses onto the entire area of said second photographic plate.

6. A method of encoding comprising the steps of: positioning a lens mosaic in face-to-face relationship with a photographic plate so that the lenses will project upon correspondingly different areas of the plate; successively projecting a difierent pattern of randomly arranged dots through the mosaic, one lens at a time, superimposing a data pattern on the plurality of said different areas of said plate, and projecting the data pattern through the different patterns of randomly arranged dots onto a common area of a display medium whereby discrete areas of the data pattern are displayed in superimposed relationship in accordance with the composite of the patterns of randomly arranged dots.

7. A method of encoding using apparatus in which a lens mosaic having N lenses is positioned in face-to-face relationship with a photographic plate so that the lenses respectively project upon N different areas of the plate, said method comprising the steps of: successively masking diiierent combinations of N -1 lenses so that the N lenses are ultimately exposed in turn; and projecting onto said N different areas of said plate a pattern of randomly arranged dots through each exposed lens that is diiferent from the patterns of randomly arranged dots respectively projected through the other exposed lenses, superimposing a data pattern onto said N different areas of said plate, and projecting said data pattern through the N patterns of randomly arranged dots onto a common area whereby discreet areas of the data patterns are displayed in superimposed apparently random relationship in accordance with the composite of said patterns of randomly arranged dots.

8. A method for recording an encoded message on a photographic plate, said method comprising the steps of: producing a photographic film negative on which N different patterns of randomly arranged dots are respectively recorded on N dififerent areas thereof; positioning a lens mosaic having N lenses in face-to-face relationship with the film negative so that the N lenses will respectively project the N patterns of dots onto the entire area of the photographic plate; and illuminating the film negative with a light image of the message to be encoded, whereby an apparently random arrangement of dots that nevertheless contains the message in coded form is recorded on the entire face of the plate.

9. The method defined in claim 8 wherein the step of producing the photographic film negative includes the steps of: positioning the lens mosaic in face-to-face relationship with the film negative so that the N lenses will project upon the N different areas thereon; and successively projecting a diiierent pattern of randomly arranged dots through the mosaic, one lens at a time.

References Cited in the file of this patent UNITED STATES PATENTS 2,794,977 Stoddart June 4, 1957 2,969,531 Stewart Jan. 24, 1961 3,018,689 Saxe Jan. 30, 1962 3,042,912 Gilbert July 3, 1962 

1. CODING APPARATUS COMPRISING: A PHOTOGRAPHIC PLATE FOR RECORDING IMAGES PROJECTED THEREON; A LENS MOSAIC HAVING N LENSES, N BEING AN INTEGER GREATER THAN 1, SAID MOSAIC BEING POSITIONED IN FRONT OF SAID PLATE WHEREAT SAID N LENSES WILL RESPECTIVELY PROJECT UPON N DIFFERENT AREAS THEREOF; MEANS FOR PROJECTING N DIFFERENT PATTERNS OF RANDOMLY ARRANGED IMAGES OF DOTS ON EACH OF THE N AREAS OF SAID PLATE, THE PROJECTION BY SAID MEANS BEING SUCH THAT THE ARRANGEMENTS OF DOT IMAGES IN SAID N AREAS ARE DIFFERENT FROM EACH OTHER, AND MEANS FOR RECORDING ON A MEDIUM IN SUPERIMPOSED RELATIONSHIP IN A SINGLE AREA A DATA PATTERN AS MODIFIED IN EACH DISCRETE N AREA BY THE RESPECTIVE ARRANGEMENT OF DOTS IN SAID N AREAS. 